national security agency is collecting billions of records of mobile phone locations from around the world every day. it is provided by edward snowden. we explain how a horrible phone can be turned into a tracking device. >> wherever you are in the world, as soon as you switch on your mobile phone, it tries to connect to the mobile network at the closest tower. when it does, your phone number is logged by the network, along with the tower you connected to, which means your location. if you're on the move, anyone with access to this information can track your route. the latest revelations suggest the n.s.a. is doing much more than just tracking individual suspects. by gathering and processing around 5 billion records each day, it is able to see which individuals are meeting or tracking together. >> you might be connected to a tower along with 100 other people. you move down the street and automatically you, fuel find connects to the next closest tower. let's say 20 of the 100 are moving the same direction you. move further down the road and say just five of the original 100 people joi